Variable inductance device



Aug. 30,. 1949.

E. c. PIERCE 2,480,671

VARIABLE INDUCTANCE DEVICE Filed Aug. 10,1946 5 Sheets-Sheet 1 IN VE/V TOR 5/65/1 5 C 55%;

4 r Tom/5 rs Aug. 30, 1949. E. c. PIERCE 2,480,671

VARIABLE INDUCTANCE DEVICE Filed Aug. 10, 1946 5 Sheets-Sheet 5 INVENTOR' fUG'ZA/E C p/ERCE wilwiw M ATTORN EYS Patented Aug. 30, 1949 STATE 5... QiEF VARIABLE.INifil oZZnUE DEVICE'. 7

Eugene C; Pierce;-Louisville, Ky; asslgnor to- 'rke Girdler Corporation, Louisville; Kygia :cou'pm tion of- Delaware Application August 10, 1946, Se'rial'N'o'. 689 ,8017

(Cl. 17Il--242') v 11 Claims. I

Thi'sflnvention'v relates to variable" inductance de'vicessuch as high frequencyhigh-power tuning coills'andhas. for anobject the provision of a coil" ofhigh electrical efi'lciencymf rugged mechanical" dsign:.and' smoothly "adjustable over. a wide range of' inductance values:

Heretofore; helical tuning cells have been proposeidin'whichthe turns of the coilhave' served asthreads inorde'r lid-advancea contact device lengthwise. of the coils. In .every'tuning' coil or variable inductance; thereis-tsome departure" in theturnsef the coilfrom a 'true helix; Accordingly', the movable contact member must provide notionly for the deviation of the coil froma true helix'i.but"also. .theremust be" provision for the maintenance. of a'go'o'd electrical contact at all times. This" is important from the standpoint ofpreventingundueheatingf If a poorelect'rica'l contact ispresentl'; arcing. and burningeffctsmay. j appear whichmay. seriously injure or abrade the conductor and therebyrender'diffl'cult or prevent."

subsequent "adjustment ortuning of "the coil;

mthepast, it'h'as been proposed to bias rolling contacts outwardly against the inner surface 01. 1

the coiled conductor to insure goodelectrical contact and also: to .provide forirregularities.in the curvature of each turn: Such 'a' roller provides a line c ontactand sometimesimore nearly a .point'. contact. "with" consequent undue. heating. thereof under "heavy: load:. When .it is considered that the'current carried by tuning. coils in high-frequencyheatlng'a'pparatus maybe of the order of 100"*amperes; it will "be" understood why many arrangements of the" prior art have .not' .proven' entlrelysatisfactory; v

In carryingout the present invention in one form thereof,;a variable inductance coll'having a plurality of turns forming a.helix:is'providediwith' a crank armwhich has'a straightporti'on which rotates ln a circular path which is concentric with themoili, Onthe straight lpOI'tiOIl' of the crank thereis disp'oseda 'contactdevlcewhich.is.slidable and rotatable with" respect "to said straight portl'on of. the crank. This contact device consists of two? side discs which extend radially outward from the straight portlon'of t'lie'cranlrarm to a pointbeyond the-widest. diameter of the cylindric'al conductor which formsthe' turns of the coil;

and preferably somewhat beyond" the remote" or" 'outer'sideoftheturm The two'discs form sup-J ports'for a. plurality'iof" spring fingcrs' arranged in a circular.array aroundeach'disc;' The fingers associated" witheach" disc" are anchored" thereto adj acentthe straight' portion" of the" crank and extend outwardlyiof' ea'c'h" disc'ih 'sp'a'ce'drelation" with the inner *surface thereof, each spring orcontactfin'ger" terminating. with an end portion? bent" toward the disc I and slidably engaging i it;-

Thus, the-arrangement provides between the two discs a-plurality of spring fingerswhich' form a good wipingelectrical' engagement along opposite sidesof the turn of the coil or helic'al conductor;

The" array of springfingersonopposite" sides 'of a turn formshort divided-"paths for current nowand for flow of heat to theheat-dis's'ipat-ing'discs;

By mounting the straight portionof the cranlr at-a'rr angle-"tome axis of the-coil; the discs and the spring fingers are-disposed for rot'a'ti'on in" a plane generally-parallel w-itl'i the pitch of the coil;

Theintermed-i'at'e portion ofthe -spring' flng'e'rs is longenou'gh to-takecareof all radial irregularitie's inthe'coll, and the resilience of' the' spring fingers not only insure's' good wipingelectricalcontact in a plurality of directions but also-provides for any axial irregularities in "the formation of "thecoil; Preferably, additional-spring fingerssecu'red to one "or both of the discs or a hub therefor extend-into re'silie'nt'engagement-with the straightpcrtl'omof the crank. 7

Timing 'coils 'c'onstructed-in'accordance with the" present invention have been found highly satisfactory'under-severeconditions of operation where the current has been in excess of amperes;--

witha frequency 'above amillion-cycles per second; specifically 614 inegaey'cles, and with relatively high radio=frequency voltages,- of the order of from '700'0 to*12;0ll0 volts.

For a more detailed understanding-of the in-- ventio'riand for further objects and advantagesthereof,- reference is to be "had to the accom= pany-ing' drawings in which:

Fig: 1 is a sideelevation of a tuning coil em-- bodying the invention;

Fig-J2 ls'an'exploded perspective view'of the portedby means of a pluralityof insulators I3 IG 0n the front" side thereof asfvie'wed in Fig; 1,

and insulators I'l-20 on the far side thereof. The lower metal cap of each insulator is suitably secured at the lower end to a base 22 and from the upper metal cap thereof has extending therefrom a lug 23, the upper end of which is brazed or otherwise rigidly secured to a narrow outer peripheral area of a selected turn of the coil. As shown, the metal caps may also support stressrelieving rings 24. Since the coil itself is constructed of relatively heavy tubing, preferably of copper or other material having a low electrical resistance, the coil may be relatively self-supporting; that is, the insulators need only be provided for approximately every third or fourth turn thereof.

In order to rotate a movable contact device 25 around the several turns of the coil, a crank 26 is provided having a straight portion 26a extending lengthwise of the coil for rotation in a generally circular path spaced from the axis of the coil. More specifically, the crank includes a straight portion in alignment with the axis of coil l and journaled in a bearing 21 carried by a bracket 28 mounted on insulators 29. Included in the drive for the crank is an insulator 33, a second bearing 3| mounted on a bracket 32, and a sprocket wheel 33. A sprocket chain 34 interconnects the wheel 33 and a driving sprocket 35 which is secured to a drive shaft 36. The shaft 36 may be drivenby hand crank or, preferablv, by a reversible motor. so that the crank 23 may be driven at will in either direction. The straight portion 26a of the crank is disposed at an angle with respect to the longitudinal axis of the coil, and at suchan angle as to incline or tilt the contact device'25 to coincide with the pitch of the coil 50., Accordingly, theleft-hand end of the straight portion 26a of the crank 26 is supported by an arm 38 carried by a bearing 39 mounted on a bracket 40 which is in turn supported by insulators 4 l. The arm 38 is not disposed in the same plane as the arm forming the crank 26, but is angularly displaced therefrom to cause the sraight portion 28a angularly to extend through the coil It; This skewed crank-shaft arrangement serves important purposes which will be later described in detail.

The contact device 25, as'best shown in Figs. 2-4, includes a hub 43 which is slidably and rotatably carried by the straight portion 260. of the crank. Though a plain'bearing is satisfactory,

' anti-friction devices may be included between the hub and the straight portion 26a, if desred. There is secured to the hub 43 thin conducting members :34 and 45, each having a plurality of I spring fingers 44a and 45a arranged in circular or radial array. The conducting members 44 and 45 are generally cup-shaped, or dish-shaped, by reason of the out-turned ends 44b and 451) thereof. They are preferably formed of berylliumcopper alloy. As best shown in Fig. 4, these outturned ends 441) and fibslidably press against a pair of discs 4'! and 48 respectively provided with shoulders Ma and 48a directed toward the hub 43 and which are held in place by suitable means, such as rivets A3. Accordingly, there is provided along the discs 41 and 48 a relatively long straight area formed by the spring or contact fingers 44a and 45a. These fingers provide for a sliding and wiping engagement with the opposite sides of the turn [0a of the coil 0. The rounded out-turned ends 44b and 45b of these spring fingers slide along the discs 41 and 48 as a turn [0a of the coil l0 departs from a true helix. The initial or unflexed position of the spring or contact fingers 44a. and 45a is substantially parallel with the discs 4'! and 43, and the fingers 44a and 4511 are spaced considerably closer together than a distance equal to the diameter of a turn Illa. Stated differently, with the contact device 25 in engagement with a turn Illa, the spring fingers 44a and 4511 are pressed away from each other to form a good wiping electrical contact with the turn lfia. Accordingly, if there is axial deviation of a turn Ella from a true helix, the spring fingers on one side of the turn will be compressed to a slightly greater degree, while the spring fingers on the opposite side will still engage the opposite side of the coil. Should the radius of a turn change, the relatively long area of the spring fingers provides for such variation without change in the good electrical contact maintained with the turn.

To provide a good electrical connection between the hub 43 and the straight portion 26a, and to avoid possibility of arcing at the bearing surface, a more or less conical conducting member or sleeve 53 is provided, which conducting member is provided with a plurality of resflient contact fingers 50a which extend outwardly from the hub 43 into sliding contact engagement with the straight portion 23a of the crank. The conducting member or sleeve 50 may be secured to the hub 43 by any suitable means, such as a plurality of screws 52, Fig. 4.

By inclining the straight portion 26a of the crank 26, Fig. 1, with respect to the axis of the coil [0, the plane of the discs 41 and 48 is tilted or disposed at an angle equal to the pitch or inclination of the turns of the 0011 I0. Accordingly, a plurality of the contact fingers 44a and 45a of the contact device 25 (as many as five or more on each side of the coil) at all times grip a turn of the coil and yet they offer a minimum of mechanical opposition to a change in position thereof upon rotation of the crank 25 by means of the drive shaft 36. There is insured at all times a substantial area of contact in contrast with a line contact or a point contact on the inner surface of the helical conductor, which point contact has heretofore been present on many tuning coil devices. The effective contact area is also increased by locating the contact fingers 44a and 45a on both sides of a turn of the coil; the several spring fingers Ma and 45a, by reason of the bending or deflection thereof, tend partly to encircle the coil Illa and thus provide area contact, in contrast with line contact, therewith. For example, in a device where the conductor of the tuning'coil i0 had a diameter of seven-eighths of. an inch, there was attained, on the average, of the order of a half a square inch of contact surface between the spring fingers and a turn of the coil. Notwithstanding this relatively large contact area, the contact device 25 could be readily moved to any desired point on any turn of the coil. More specifically, as the drive shaft 36 is rotated to rotate the crank- 26, the frictional engagement between the contact members or fingers Ma and 45a causes them to rotate with respect to a turn of the coil and with respect to the straight portion 26a of the crank 26. This rolling-wiping contact engagement is important to the present invention since it has proven to be a highly desirable feature. The rolling-wiping contact surface of the device 25 constantly changes during adjustment along a turn of the coil, and there is thereby assured a good, clean electrical contact. of low resistance. The wiping and cleaning action on each contact finger occurs radially thereof as well as from side to side. The action is in all directions over thefl'surface of the contact fingers andz'withi. respect-to. the turn of the coil: so that. there is.

assured-a goodielectrical and thermal:engagement betweenthefingers andthe turn ofithecoilu The skewed" arrangement with the narrow. contact discs-permits. a reduced spacing-iota the-turns and thus better. Q values may be obtained; By reducing-the pitch; the frictional" resistance is also,

decreased.

By; connecting-one end of the coilto the-.con-

duotor Hyanynumber-of turns of the .coil. 10,501.

any-sfraction: or. a; turn, may: be. included in a. cire cuit extending. between the conductors ll and-ithe terminalzmember l2 which leadsto the other-con- The terminal member I Z 2 isrfastened as by a screw 53 to a plate.54 which ductor of: the circuit.

is electrically connected to a pluralit of spring fingers 55 which resiliently form a wipingcontact engagement with conductor forming the bearing supportedipart of: -ie crank Thus, if: the

contact device by suitable rotation of the drive shaft 36 is moved tothe right-handrend of the Though. devices embodying the invention have satisfactorily carried loadsupwardiy of imam-- peres over substantial periods oftime without damage, higher loads may ofcourse 2e safely car.- ried by. increasing the size of the conductors and of the contact assembly 25. other tuningcoil arrangements, the present invention indicates that for a comparable size of.

conductors, there is attained a surprisingly large increaseof, current capacity, as much. as seventyper. cent, The heat-=radiating capacity or the.

movable contact assemblyv is evengreater, and.

more of -theorder of three hundred per cent oh that in comparable devices of the prior art due.

to the increased current-carrying ability. The unusual. increase in the heat-radiating capacity is duetc a number of factors. For example, the multiplicit of spring. fingers or contact members arespaced from the discs. and- ;to provide a maximum radiationarea. Thereis -little thin terfere with thermal circulation of airaround the; contact fingers which assists incarrying awayany heat which may develop. When heat does. de-.

velop in the. contact fingers, it readily-flows;

through the multiple and relatively short heat-.

conducting paths to the discs 41 and 48 which provide additional andrelatively large heat-dissipating surfaces for rapid dissipation thereof as by-radiation.

Referring to Figs. 5 and 6, thereis illustrated a-modified form of the contact devica; which-may; be, taken-as suggestive of other forms of the invention which may he; made; within the scope of the appended claims. For example, the two supporting-members ordi cs 5S and 6-} of aluminum have beendesigned sothat the inner-sur faces 60aand iila slope outwardly from adjacent the hub 62 to provide the necessary clearances.

along the radial lengths of the respective contact fingers: Maanda. By having thetwo; discstii.

nd-ti flerineputwarmr rom he 1ub;5. .;room.-

Incomparison with is provided for a plurality of; heat-radiating :and;% dissipatin fins 60a and 61a, without increasingthe-overall axial dimension of the assemblyine:

eluding thediscs andtwit'hout reducing-the space: between eachzdisc and. the-adjacentrturn of the: coil; 1 'Ihesev fins 60a and' 61 ware iormediinward lyof each disc and; asshownin Fig. 5, the outer surfacesthereof aresubstantially in the plane. otthediscs. The finsare-spaced onefrom-etheother and fromtthe periphery of the discs toward-'- the-hub-have gradually increasing areas. The

contact fingers a and 45a are spacedsubstantially from the angularly disposed inner faces-0F thediscsfill and-6i so=that ample room is provided for deflection -of=the fingers to take care 0f'-their wiping andcleaning engagement with theturnofthe conductor andalso to provide for deflection to take careof any variation in diam eter of theconductorofthecoil.

Further inaccordancewith Fig. 5, two circular arrays of contact fingers 64 and a are provided at:therespective-endsof the hub 62, these-ter minatingat the huhEZ-in out-turned flanges 64a and 65a which are disposed between shoulder- OfIthehub-GZ and the-discs fill and-Si. Since the conductorsof contact fingers Ma and 64 -(and 45a and 65) are in abutting and overlapping contact with each other, thereis provided a directelectrical-path from the-conductor of the coil through the contact-fingers-Ha and 45a to the: con-tast fingers 64 and 65 which= completethe electrical connection-to-the crankarm. By-providingthe-double array of contact fingers 64' and 65; a. centering action is attained and the contact sliding engagement, thus insuring a-maxi1num= cleaningactionanda minimum electrical resistance.

The assembly and disassembly of the contact device is readily accomplished by the removal of a few' bolts, generall four, three of which, the bolts 68e-70appear in Fig. 5, and the other of which, the-bolt?!" alsoappears in Fig. 6. Thesethru-bolts clamp all of the parts together and form the sole-fastening means to provide a rugged-:assembly of thecontact device.

While preferredembodiments of the invention havebeen fully describechit is to be understood; thatmodifications-may be made withinthe scope ofithe appended claims which set forth those features which distinguish it from other inventions and which are distinctly-claimed as character-- izingthepresent invention.

What is claimed is:

1. In variable inductance coil having a pluralityof'turns forming a helix and a crank having a straight portion extending lengthwise of said coiland inclined with respect-to the longi-- tudinal aXisof said coilfor rotation in a circular path'about-said axisof said coil, the combination of' contact means for said-coil comprising two discsidisposed onopposite sides ofa turnof saidcoil: androtatably carried by said straight .portion, ,andga. plurality/of springfingers respectively anchored tosaid' discs adjacent said straight porfrom for resilient engagement with opposite sides of a turn of said coil, rotation of said crank pro ducing relative rotation between said discs and spring fingers as a unit with respect to a turn of said coil and along said straight portion progressively to change the electrical connection from said crank to said coil with a minimum of mechanical effort.

2. In a variable inductance coil having a plurality of turns forming a helix and a crank having astraight portion angular-1y extending lengthwise of said coil for rotation in a circular path spaced from the axis of said coil, the combination of contact means for said coil comprising a hub rotatably and slidably mounted on said straight portion, a plurality of contact fingers extending from said hub into resilient contact engagement with said straight portion, a pair of discs disposed on opposite sides of said hub and extending outwardly therefrom into overlapping engagement with a turn of said coil, and a plurality of spring fingers respectively anchored to each of said discs and to said hub and in circular array extending outwardly from said hub toward the peripheries of said discs, the outer ends of said spring fingers being bent respectively toward their associated disc to space the intermediate portions therefrom for resilient wiping engagement with the opposite sides of a turn of said coil, rotation of said crank producing rotation of said circular array of spring fingers with respect to said turn of said coil to change the electrical connection along said turn and to change the contact fingers engaging the opposite sides of said turn.

3. In a variable inductance coil formed by a helical conductor, contact means therefor comprising discs spaced apart a distance greater than the outside diameter of the conductor of a turn of said coil, to circular arrays of resilient contact fingers respectively having their outer end-portions slidably engaging the peripheral portions of said discs and means for anchoring the inner endportions of said arrays of contact fingers to provide intermediate portions disposed for resilient wiping contact engagement with a turn of said coil.

4. A continuously variable inductarice comprising spaced turns of a conductor formed into a helix, a shaft spaced from and rotatable about the axis of said helix, contact structure rotatably and slidably mounted on said shaft comprising a pair of cup-shaped spring contact members spaced to press against opposite sides of said conductor and of diameter insuring their continued engagement with said sides of said conductor for all positions of said shaft and notwithstanding variations in diameter of said helix, and a pair of backing discs thermally, mechanically and electrically engaging said members throughout the outer peripheries thereof.

5. In a variable inductance coil having a plurality of turns of a conductor formed into a helix and a crank arm rotatable within said helix, the combination of a heat-radiating current-carrying contact means comprising two members, rotatable and slidable with respect to said crank arm, spaced apart a distance somewhat greater than the axial dimension of said conductor, said members providing a substantial area for dissipation 01, heat therefrom as by radiation, and a plurality of spring fingers carried adjacent corresponding ends thereof by said members, their opposite ends being bent towards and slidably engaging said members to provide resilient contact areas for engaging opposite sides of a turn of said coil, the spring fingers engaging a turn of said coil providing dual heat-conducting and current-carry ing paths for fiow of heat and current to said heat-dissipating members.

6. In a variable inductance coil having a plu= rality of turns of a conductor formedinto a helix and a crank arm rotatable within said helix, the combination of a heat-radiating current-carrying contact means comprising two members, ro tatable and slidable with respect to said crank arm, spaced apart a distance somewhat greater than the axial dimension of said conductor, said members having a plurality of heat-radiating fins providing a substantial area for dissipation of heat therefrom as by radiation, a plurality of spring fingers disposed in circular array between said members, and means supporting the inner portions of said fingers in heat-conductive relation with said members, the opposite outer ends of said spring fingers being bent towards and slidably engaging said members to provide intermediate resilient contact areas for engaging opposite sides of a turn of said coil, a plurality of said spring fingers simultaneously engaging a turn of said coil to provide dual and relatively short heatcenducting and current-carrying paths for flow of heat and current to said heat-radiating members.

'7. A variable inductance comprising a con ductor in the form of a helical coil of substantially uniform diameter, a crank arm having a straight elongated member spaced outwardly from the axis of said coil, extending longitudinally of said coil, and supported for rotation in a circular path generally concentric with said coil, a contact device carried by and rotatable relative to said member and longitudinally movable along said member while electrically connected thereto, said contact device having a plurality of resilient contact fingers disposed in circular array around said elongated member and extending radially outward therefrom for resilient engagement with a side of said conductor which faces toward one end of said coil to complete a low-resistance connection thereto and to propel said contact device in one direction, said fingers successively engaging said conductor as said contact device rotates relative to said elongated member of said crank arm and as the latter rotates relative to said coil, and structure carried by said contact device engaging the side of said conductor facing toward the other end of said coil for propelling said contact device along said elongated member in the other direction to follow the turns of said coil.

8. A variable inductance comprising a conductor in the form of a helical coil of substantially uniform diameter, a crank arm having a straight elongated member spaced outwardly from the axis of said coil, extending longitudinally of said coil, and supported for rotation in a circular path generally concentric with said coil, a contact device carried by and rotatable relative to said member and longitudinally movable along said member while electrically connected thereto, said contact device having a plurality of resilient contact fingers disposed in circular array around said elongated member and extending radially outward therefrom for resilient engagement With a side of said conductor which faces toward one end of said coil to complete a low-resistance connection thereto and to propel said contact device in one direction, said fingers successively engaging said conductor as said contact device rotates relative to said crank arm member as the latter rotates relative to said coil, and a second circular array of contact fingers extending radially outward from said contact device for resilient engagement with the side of said conductor facing toward the other end of said coil to complete a low-resistance connection thereto and to propel said contact device in the other direction and to follow the turns of said coil.

9. In a variable inductance coil having a plurality of turns forming a helix and a crank having a straight portion extending lengthwise of said coil and inclined with respect to the longitudinal axis of said coil for rotation in a circular path about said axis of said coil, the combination of a contact device carried by said straight portion comprising two discs extending outwardly from said straight portion on opposite sides of a turn of said coil and rotatably carried by said straight portion, resilient cup-shaped contact members respectively between said discs and said opposite sides of said turn of said coil and each mechanically and electrically in engagement with one of said sides and with one of said discs, rotation of said crank producing relative rotation of said discs and said contact members progressively to bring different parts of said contact members into wiping engagement with said opposite sides of said turn of said coil as said relative rotation progressively moves said contact device along said turn of said coil.

10. In a variable inductance coil having a plurality of turns forming a helix and a crank having a straight portion angularly extending lengthwise of said coil for rotation in a circular path concentric with and spaced from the longitudinal axis of said coil, the combination of contact means for said coil comprising a hub rotatably and slidably mounted on said straight portion, a pair of discs supported from said hub and extending outwardly therefrom into overlapping relation with a turn of said coil, and a plurality of spring fingers disposed in circular arrays about said hub and respectively between said discs and the opposite sides of the turn of said coil for making electrical and thermal contact with said turn of said coil and with said discs, the outer ends of said spring fingers being bent respectively toward their associated discs to space the intermediate portions therefrom for resilient wiping engagement with the opposite sides of a turn of coil, rotation of said crank producing rotation of said circular array of spring fingers with respect to said turn of said coil to change regions of thermal and electrical contact with said turn and to change the contact fingers engaging the opposite sides of said turn.

11. In a variable inductance coil formed by a helical conductor, contact means therefor comprising discs spaced apart a greater distance than the outside diameter of the conductor of a turn of said coil, two circular arrays of resilient contact fingers respectively having their outer end portions slidably engaging the peripheral portions of said discs, means for anchoring the inner end portions of said arrays of contact fingers to provide intermediate portions disposed for resilient wiping contact engagement with a turn of said coil, and means rotatably supporting said anchoring means for rotation of said arrays of contact fingers concurrently with circumferential movement thereof along said helical con-. ductor from one position to another.

EUGENE C. PIERCE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,831,375 Adams Nov. 10, 1931 2,367,922 Bock Jan. 23, 1945 2,425,411 Zottu Aug. 12, 1947 

